Technical Field
The present disclosure relates generally to the field of combustion furnaces and methods of use, and more specifically to processes for producing hollow glass fiber or glass fibers comprising bubbles using a turbulent submerged combustion melter, and burners for carrying out such processes.
Background Art
In submerged combustion melting of glass and similar materials, combustion gases emitted from sidewall-mounted and/or floor-mounted burners are injected beneath the surface of a molten or partially molten mass of material being melted in a melter vessel and rise upward through the molten or partially molten mass. The molten or partially molten mass of material is a complex mixture of molten feed material (feed material is commonly referred to as “batch” in the glass industry), unmelted batch, and gases from the burners and evolved gases from the reaction of and/or decomposition of batch materials. Recycled glass or “cullet”, as well as various waste materials of varying glass content (such as fiberglass batting or even loose fibers) may also be present. The materials are heated at a high efficiency via the intimate contact with the combustion gases. Using submerged combustion burners produces turbulence of the molten material or partially molten material. Vibration of the burners and/or the melter vessel walls themselves, due to sloshing of molten material, pulsing of combustion burners, popping of large bubbles above or aside of submerged burners, ejection of molten material from the melt against the walls and ceiling of melter vessel, and the like, are possible.
Traditional methods of making hollow fibers employ a bushing and a source of air feeding the air into the molten glass as it passes through a bushing. U.S. Pat. No. 2,269,459 discloses using a tube for injecting air into molten glass discharging vertically downward from a vessel, the tube extending through a bushing on the bottom of the melter. The initial hollow fiber formed is then drawn through and heated in a burner that provides intense flame and heat to form a much smaller diameter hollow fiber. Bushings are described in a series of patents for making fibers having intermittent hollowness along their length, as well as hollow glass fibers of more uniform hollowness, more ratio of ID/OD, and better concentricity of the central lumen. See U.S. Pat. Nos. 3,421,873; 3,510,393; 3,268,313; 4,735,642; and 4,758,259. None of these patents use or discuss submerged combustion. None of the previous solutions have recognized that submerged combustion produces a turbulent molten glass that has approximately 40 percent by volume gas bubbles. In fact, traditional glass melting technologies seek to reduce bubble content when making glass fibers, as it leads to frequent processing problems due to fiber breakage during drawing. Molten glass fining is called for to reduce or eliminate bubbles, the fining employing conditioning channels that may be difficult and/or expensive to operate.
It would be a significant advance in the glass melting art to develop processes of making hollow glass fibers, or solid glass fibers having entrained bubbles therein, and apparatus and systems to make such fibers.